How to make image texture transparent
JPEG does not support alpha channels. This will mean that the Alpha returned by the Image Texture node will be a constant 1.0.

The only simple solutions will be to either convert your image to a PNG or similar and add an alpha channel or to use the properties of the image to simulate alpha - for example, if the ‘background’ is pure black and the curtain doesn’t contain any black then simply use a Greater Than node set to 0.0 to generate “alpha” directly from your color data (ie, wherever Color is not 0.0 you’ll get 1.0 for alpha).